Alloy



' erties by thermal treatments, alloys having.

Patented June 23, 1936 v UNITED 'ISTATES PATENT, OFFICE 2,045,238 ALLOYRoy E. Paine, Oakland, Calif., assignor, by mesne assignments, toMagnesium Development Corporation, a corporation of Delaware No Drawing.Original application October 4,

1933, Serial No. 692,132. Divided and this applioation November 15,

1935, Serial No. 49,962

1 Claim. (01. 75-168) The art of casting magnesium presents manypractical difliculties which must be surmounted before the truecommercial possibilities of mag nesium castings can be fully realized.An alloy which is suitable for one application may be entirely unsuitedto another and, as a consequence, it is frequently necessary tosacrifice desirable characteristics of the alloy in order to more fullyrealize the advantages of some one or more important characteristics.Thus a compromise must quite frequently be made in order to approach inone alloy the optimum properties for a given application. For example,it may be found that corrosion resistance can be sacrificed to a certainextent to obtain higher tensile strength, yield point, hardness, orsimilar mechanical properties. Again, tensile strength may be sacrificedin order to obtain proper casting or working characteristics. It is anobject of the present inven-' tion to-develop magnesium alloys whichwill combine to a maximum degree the characteristics of corrosionresistance, favorable mechanical properties, workability, susceptibilityto improvement by heat treatment and adaptability to sand casting.

A further object is the provision of magnesium alloys characterized bytheir susceptibility to be improved in mechanical properties by suitablethermal treatments. A further objectis the provision of magnesium-basealloys characterized by 1 good corrosion resistance in either the castor in the cast and heat treated condition. A further object is theprovision of magnesium alloys possessing excellent castingcharacteristics. A further object is the provision of magnesium-basealloys susceptible, within certain ranges, to mechanical deformation.

I have discovered that magnesium-base alloys containing from 0.5 percentto.22 per cent of lead possess to an appreciable degree the collectivecharacteristics of alloys which are resistant to corrosion, alloys whichmay be readily cast, alloys which are susceptible to alteration ofpropfavorable mechanical properties, and alloys which, within arestricted rangeymaybe worked 7 by extrusion, forging, or other means ofmechanical deformation.

In accordance with my invention lead may be present in amounts as low as0.5 per cent; The

preferred casting alloys are those containing above about per cent oflead since it is in these alloys that the most pronounced combination ofthese different properties is obtained. The

alloy may be worked by extrusion over a range of from about 0.5 per centto about 22.0 per cent of lead. As an all around casting alloy I havefound a magnesium alloy containing 5 to 10 per cent of lead to beparticularly adapted to general foundry purposes. Alloys falling withinthis preferred range of composition as well as other alloys comprisedwithin the broader limits previously defined, have been subjected tosevere tests designed to produce accelerated corrosion. Sand cast testbars poured in accordance with the best casting practice in the art weresubjected to corrosion tests in the as cast and in the heat treatedcondition. In the example referred to the heat treatment was carried outat about 459 centigrade for about 20 hours followed by quenching inwater, and both heat treated and unheat treated test bars were subjectedto that corrosion test which comprises alternately immersing the metalin, and removing it from, a 3 percent sodium chloride solution for about80 hours, a treatment referred to hereinafter as the alternate immersiontreatment. I

There are certain elements which may headded to the binarymagnesium-lead alloys to par- I ticular advantage.

Such, for instance, are the metals calcium, cadmium and zinc. be addedsingly or in combination with each other, the zinc in amountsbetweenabout 1.0 per cent and 10.0 per cent, the calcium between about 0.1' percent and 2.0 per cent, and the cadmium between about 1.0 per cent and10.0 per cent. These alloying elements are substantial equivalents asindicated by their susceptibility to thermal treatment in magnesium-leadalloys. The calcium favorably affects the casting properties of thealloy without markedly decreasing its corrosion resistance. Forinstance, a magnesium alloy containing 21.4 per cent of lead and 0.25per a strength loss of only 17 per cent after alter- These may nateimmersion in a 3 per cent sodium chloride solution for about 80 hours,while a heat treated magnesium .alloy containing. about 5 per cent oflead to which about 0.25 per cent of calcium had been added did notundergo any appreciable loss in strength under the foregoing corrosionconditions; the heat treatment in this case was a treatment at about 450centig'rade jfor about 20 hours.- An alloy of magnesium with about 5.1percent of lead and 10.0 per cent of cadmium had in the sand castcondition a tensile strength of about 24,650 pounds per square inch andan elongation of about 9.8 per cent' in 2 inches. After a heat treatmentof about 20 hours at about 450 centigrade its tensile strength hadincreased to about 25,140 pounds per square inch and its elongation to10.3 per cent in 2 inches. After an alternate immersion corrosion testfor 80 hours the loss in strength was only 30 per cent. I A similarresult was obtained with a magnesiumbase alloy containing about 5.3 percent of lead and about 5.0 per cent of cadmium. An alloy of magnesiumwith about 5.0 per cent of lead and 5.0 per cent of zinc had in the sandcast condition a tensile strength of about 23,370'pounds per squareinch. After a thermal treatment of about 20 hours at 450 centigradefollowed by an aging treatment of about 20 hours at 150 centigrade itsstrength had increased to about 25,710 pounds per square inch. After analternate immersion corrosion .test of 80 hours the loss in strength wasonly 12 per cent. Another alloy of magnesium with about 5.2 per cent oflead and 3.2 per cent of zinc under similar conditions lost only about10 per cent after 80 hours alternate immersion in the corrosivesolution. As a preferred composition for alloys of this nature I advise(1)- 5.0 per cent lead, 1.0.per cent calcium, balance magnesium; (2) 5.0per cent lead, 5.0 percent cadmium, balance magnesium; (3) 5.0 per centlead, 50 per cent zinc, balance magnesium. If more than one of theelements calcium, cadmiunnor zinc be present simultaneously, I prefernot to exceed a total of 10.0 per cent for these elements. I g 7 One ofthe disadvantages of the alloys described herein which'may affect theiruse in certain applications, particularly where high strength is a thealternate immersion treatment.

.per cent of its strength.

also in surface hardness. An alloy of this nature containing about 8.0per cent of lead and 0.85 per cent of manganese lost.only 6 per cent ofits originalstrength after 80 hours alternate immersion in a 3 per centaqueous solution of sodium chloride and in the solution heat treatedcondition lost only 7 per cent of its strength in A magnesium alloycontaining about 10.37 per cent of lead had lost only about 10-per centof its strength 10 at the expiration of this period as compared withcertain other commercial alloys, such as, for instance, the well knownmagnesium alloy containing about 7 per cent of aluminum and 0.4 per centof manganese which, at the end of 15 hours of alternate immersion, hadlost about 60 Very favorable alloys can be compounded by using as a basean alloy of magnesium, lead and aluminum and making additions thereto ofat 20 least one of the class of metals tin, manganese or leading orvery'material consideration, is the fact I that the grain structure ofthese alloys (with or without calcium) tends to becoarse. I have foundthat the metals aluminum and silicon'form a class of alloying elementswhich may be added to. magnesium-lead alloys andare, substantiallyequivalent in this respect that they materially refine the grainstructure of the alloy. Aluminum, for instance, can be added over awide'range, such 1.0 and 15.0 per cent; silicon may be as betweeneffectively present for this. purpose in amounts of about 0.1. to 2.0percent. When .used in combination it is advisable that the totalcontent of aluminum and silicon does'not exceed 15.0 per cent. In thepreferred practice of my invention I have found that the best resultsare usually obtained when the aluminum is present in amounts between 5and 10 per cent.

As a preferred magnesium-lead-silicon composltion Iluse a magnesium-basealloy containing 7.0 per cent of lead and 0.5 per cent of silicon. As apreferred magnesium-lead-aluminum alloy I use a magnesium-base alloycontaining 7.0 per cent of lead and 5.0 percent of aluminum. When thealuminum and silicon are used in tion Iprefer to use a total of about5.0 per cent of.aluminum' and silicon combined, for instance about 4.0per cent aluminum and 1.0 per cent silicon.

Manganese alone may be added to magnesiumlead alloys in amounts between0.1 per cent and 1.0 per cent and has a stabilizing effect upon thealloy properties in that it raises the hardness slightly, does notmaterially decrease the corrosion resistance, and adds to the matrix ofthe alloy a hardening element which expresses itself not only in anincrease in tensile strength but zinc. The lead can be used in amountsfrom. about 0.5 per cent to about 22.0 per cent, the aluminum from about1.0 per cent to about 15.0 per cent, the tin-from about 1.0 per cent toabout 25 15.0 per cent, the manganese from about 0.1 per cent to about1.0 per cent, and the zinc from about 1.0 per cent to about 10.0 percent. A sand cast alloy within this range had, in the as cast condition,a tensile strength of 27,500 pounds per square inch and an elongation of5.7 per cent in 2 inches. After a thermal treatment of 16 hours at 315centigrade, the alloy had a tensile strength of '29,640 pounds persquare inch and an elonga- Some of the tion of 6.0 per cent in 2 inches.heat treated specimens were then given an alternate immersion treatmentfor 40 hours and after the treatment the specimens had a tensilestrength of 28,413 pounds per square inch and an elongation of 5.8 percent in 2 inches, this alloy containing 5.0 per cent of aluminum, 5.0per cent of lead, 0.4 per cent of manganese and 2.0 per cent of zinc.The lfiss in strength on the corrosion treatment is observed to be lessthan 5 per centas balance magnesium; (3) 7.0 per cent lead, 7.0

per cent aluminum, 2.0 per cent tin, 2.0 per cent zinc, balancemagnesium.

Two alloy compositions within this range which I have used to advantageare as follows: A magnesium base alloy containing 8.0 per cent of aluvminum, 3.0 per cent of lead, 0.4 per cent of mangam 7 nese, 1.0 per centof zinc, and 3.0 per cent of tin; a magnesium-base alloy containing 8.0per cent of aluminum, 1.0 per cent of lead, 0.4 per cent of manganese,1.0 percent of zinc, and 1.0 per cent oftln.

The addition of lead to the magnesium-aluminum-manganese alloysincreases very considerably the corrosion resistance of these alloys,since with the addition of about 7 per cent of lead to an alloycontaining 7 per cent of aluminum and l 70 per cent of manganese, theloss of strength after the alternate immersion test was only about 30per cent, as compared with about 60 per cent of the same alloy withoutlead.

Alloysof magnesium with lead, aluminum, and 76 manganese have beendisclosed hereinabove. have discovered that if to a base alloy ofmagnesium-lead-aluminum-manganese I add one or more of the class ofmetals calcium or cadmium, the resulting alloys become considerably moresusceptible to variation of properties by thermal treatments and theirhardness can be markedly increased by artificial aging after thermalsolution treatments. In these alloys the. lead content should range fromabout 0.5 per centvto 1 about 22.0 per cent, the aluminum from about 1.0per cent to about 15.0 per cent, and the manganese from about 0.1 percent to about 1.0 per cent. To these elements as a common base I add theelements calcium, or cadmium, singly or in combination, the calcium inamounts fromabout 0.1 per cent to about 2.0 per cent, the cadmium fromabout'1.0 per cent to about 10.0 percent. As an example of an alloyofthis nature, a sand cast specimen of a magnesium-base alloy containingabout 10.0 per cent of lead, about 7.0 per cent of aluminum, about 0.4per cent of manganese, and about 5.0 per cent of cadmium, had in thecast condition a tensile strength of about 23,200 pounds per squareinch. After a thermal solution treatment of 21 hours at about 430centigrade the tensile strength of the alloy had increased to about36,000 pounds per square inch, a. gain in strength of about 55 per cent.The same alloy after the solution treatment had a Brinell hardness ofabout 61 and this hardness was, raised to about 84 by an additionalaging treatment of '20 hours at about 175 centigrade, the tensilestrength increasing slightly to. about 37,000 pounds per square inch.

Similarly, a magnesium-base alloy containing about 5.0 per cent of lead,7.0 per cent of aluminum,'10.0 per cent of cadmium, and 0.4 .per' cent-of manganese had in the sandcast condition a tensile strength of about24,000 pounds per square inch. After a thermal treatment of 21 hours atabout 430 centigrade the alloy had a tensile strength of about 35,000pounds per square inch. An additional aging treatment raised the Brinellhardness of the alloy from about 61 to about 79.

Similarly, a magnesium-base alloy containing about 5.0 per cent of lead,10.0 per cent of cadmium, 7.0 per cent of aluminum, 1.0 percent ofmanganese, and 0.25 perv cent of calcium had in the sand cast conditiona tensile strength of about 24,290 pounds per square inch. After athermal treatment of hours at about 430 centigrade this alloy had atensile strength of about 33,200 pounds per square inch. After anadditional thermal treatment of about 20 hours at about 150 centigradethe strength increased to about 35,600 pounds per square inch. and theBrinell hardness from about 47 to about 66.

Another magnesium-base alloy containing about.10.0 per cent of lead, 7.0per cent of alu minum, 5.0 per cent of cadmium, 0.4 per cent ofmanganese, and 0.1 per cent of calcium, had in the sand cast condition atensile strength of about 23,210 pounds per square inch. After -athermal solution treatment of 21 hours at about 430". centigrade thealloy had a tensile strength of about 36,030 pounds per square inch; theBrinell hardness was about 61. Afteran additional aging treatment ofabout 20 hours at about 175 centigrade its tensile strength was about37,010 pounds per square inch-- and its Brinell hardness about 84. As adesirable alloy of this nature I advise 7.0 per cent lead, 7.0 per centaluminum and 0.4 per cent manganese. If more than one of the elementscalcium or cadmium are present simultaneously, the total should not 5exceed about 10.0 per cent for preferred purposes.

The addition of zinc in amounts from about. 1.0 per cent to about 10.0per cent to magnesiumlead alloys containing aluminum and silicon incombination decreases the linear shrinkage, thus favorably affecting thecasting properties, and also increases the corrosion resistance andraises the yield point of these alloys. In alloys of this type the leadshould range from 0.5 per cent to 15 22.0 per cent, the aluminum from1.0 per cent 15.0 per cent, and the silicon from 0.1 per cent to 2.0 percent, but the total amount of aluminum and silicon should preferably notexceed 15.0 per cent; 20

A- useful alloy of this nature is a magnesiumbase alloy containing about10.0 per cent lead, 8.0 per cent aluminum and 3.25 per cent zinc.Another useful composition is attained by substituting about 1.0 percent silicon 'for part or all of the aluminum.

An alloy similarly improved in casting properties, although not to sucha decided extent, is one containing from about 0.5 per cent to 22.0 percent of lead, from about 1.0 per cent to about 10.0 per cent of zinc,.and from about 0.1 per cent to about 2.0 per cent of silicon. Afavorable alloy within this range is a magnesium-base alloy consistingof about 10.0 per cent of lead,

about 3.25 per cent of zinc, and about 1.0 per cent. of silicon, thebalance being substantially magnesium.

In making up alloys of the compositions disclosed hereinabove the alloysmay be compounded by any of the methods known in the art. 40

In casting the alloys recourse may be had to the protective measuresdisclosed in existing patents and the publishedtliterature relating toeasily .oxidizable metals- 'The alloys, especially the magnesium-leadbinary alloys, may be extruded over the entire disclosed compositionrange, but other types of mechanical deformation such as rolling orforging. should be carried on with due regard for the fact that. as thepercentage of total added alloying elements increases, the necessity forprecaution in working the alloy also increases.

It is my object to retain, as far as possible, the advantages of the useof magnesium base, such as low specific gravity, while securing inaddition the hereinabove disclosed'benefits accruing from the additionsof the other alloying elements herein outlined. Accordingly, where inthe appended claims the term magnesium-base alloy is used, it refers to.analloy containing more than approximately 50 per cent of magnesium.-This application is a division of my copending application SerialNo.692,132, filed October. 4, 1933. n

' A magnesium base alloy containing from about 0.5 to about 22.0 percent of. lead, from about 1.0 to about 10.0 per cent of cadmium, andfrom about 1.0 to about 10.0 per cent of zinc, the balance beingmagnesium.

, ROY E. PAINE.

